Herd Pregnancy Testing - How accurate are we?!

November 29, 2018

By Rachel Numan, Te Awamutu

With the end of mating drawing to a close, the next item on your animal health agenda will probably be your herd pregnancy test. Many of our clients can’t stand the suspense of waiting for results, and will do two scans – an early and a late one. An early scan is usually done 12 weeks after the start of mating, and the final scan 6 weeks after the bull has been out of the herd.

Good reasons to do two scans include:

Accurate calving dates: with an early scan, every cow will have an assigned calving date. The benefits of this are the ability to dry off based on calving date (and therefore gain more days in milk); a higher value of any sale animals if they have a specified AB calving date; and better transition management in the pre-calving period.

Feed budgeting and early culls: with a predicted dry summer, it is good to know who your late calvers will be earlier in the season so you can destock early and still get good cull prices at the works. Accurate calving data will also allow for better feed budgeting coming into next spring.

Two scanning dates will also give a more detailed fertility focus report. This means that if you want to improve your herd reproduction, we have better data and can pinpoint where you might be able to make changes.

At the second scan, we usually only scan the cows who were not visibly pregnant at the first scan. So it’s not a case of scanning the entire herd twice – and if you had great AB results, then there might be very few cows to scan a second time!

In terms of how accurate rectal ultrasound pregnancy diagnosis is, in 2016 a New Zealand study following 12 experienced veterinarians and 83,104 cows was published. The study looked at when the cow calved compared to her predicted calving date based on scanning results. The study showed that over 90% of cows calve within 10 days of their predicted calving date. Having access to the AI history of the cow increased accuracy (which is why it is so important to be signed up to infovet), and having multiple AI dates decreased the accuracy of the scan. An early scan allows better differentiation between multiple inseminations in the same cow, so if you are wanting accurate dates definitely consider ringing us to book in an early scan.